Railway track circuit apparatus



Dec. 8, 1936. A, E, DODD 2,063,300

RAILWAY TRACK CIRCUIT APPARATUS Filed NOV. 8, 1954 2 Sheets-Sheet l A z, 1 a )2 2 7 20 L2 1 1 I. 1. 5% P 4 7 Pfi 25 1 E 4 224% C x I 1 Y V yl 1 14 L n- .7. .S{ L g AINVENTOR HIS ATTORNEY Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE RAILWAY TRACK CIRCUIT APPARATUS Application November 8, 1934, Serial No. 751,970

21 Claims.

My invention relates to railway track circuit apparatus, and has for an object the provision in apparatus of this character of a track relay combination which can be adjusted to provide,

as nearly as possible, maximum shunting sensitivity under the infinite ballast resistance condition. I accomplish this result by providing a track relay combination which can be adjusted to pick up and release on, as nearly as possible,

1 the same values of current and voltage. My invention is particularly applicable to track circuits having a neutral track relay which controls a polarized line relay situated at the same location.

I will describe several forms of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawings, Fig. l is a diagrammatic view showing one form of track circuit apparatus embodying my invention. Figs. 2 to 14, inclusive, are views similar to Fig. 1, but each showing a modified form of relay combination also embodying my invention. Fig. 15 is a diagrammatic view showing some construction details of a portion of the apparatus illustrated in the other figures of the drawings.

Similar reference characters refer to similar parts in each of the views.

Referring first to Fig. l, the reference characters i and l designate the track rails of the railway track, which rails are divided by insulated joints 2 to form a track section AB. A source of current C is connected across the rails at one end of this section through a current limiting resistor R, this source, as here shown, being a battery. Located at the other end of the section is a primary relay P and a secondary relay S. The primary relay P may be a neutral track relay of usual construction except for the manner of inter-connecting the two coils 3 and 4 of the relay which matter will become more clear as the description progresses. The secondary relay S is of the polarized type, having both neutral and polar contacts. The distinctive feature of relay S is that its neutral armature is retained or prevented from releasing during the pole-change interval; that is, neutral back contact 5 does not close during a reversal of polar contact 6. Winding 1 is the operating winding of relay S, whereas 9 is the retaining winding,

and the latter receives its energy from a winding 8 which is inductively coupled with winding i.

One type of secondary relay S suitable for use in this connection is that shown diagrammatically in Fig. 15, oi the d awings and described at another point in the specification. This type of relay is well known to those versed in railway signaling.

The primary relay P is provided with a pickup circuit which is connected across the rails l and 5 l and this circuit passes from rail I, through the left-hand coil of relay P, wire [0, back contact 5 of relay S, and the right-hand coil 4 of relay P to rail l Relay P is also provided with a holding circuit which passes from rail I, coil 10 3 of relay P, wire H, resistor R and the upper portion of coil 4 of relay P, back to rail l It will be seen from the foregoing that the pickup circuit for relay P includes the entire operating winding of this relay, whereas the holding cir- 15 cuit includes only a portion of the operating winding and a resistor R which compensates for the reduced resistance of the relay winding and also alters the time constant to aid in making the relay P quick releasing.

The secondary relay S has an energizing circuit which includes front contact l2 of relay P. The current for relay S flows over a pair of line wires XY from a battery which is not shown but which will ordinarily be situated at the next signal location in advance, so that current of the proper polarity in accordance with trailic conditions in advance will be supplied to relay S in a manner well-known in the railway signaling art.

The primary relay P is preferably a relatively low resistance relay having normal pick up and release characteristics, and may for example, be a standard 4 ohm track relay. The secondary relay S is preferably a relatively high resistance relay having slow pick up characteristics due to its peculiar structure, and may for example, be a 50 ohm relay. Relay S is provided with additional contacts such as 6 and. I3 which may be used to control circuits for signals or any other desired traffic governing apparatus.

The operation of the apparatus shown in Fig. 1 is as follows: Normally, both relays P and S are picked up, so that the holding circuit for relay P is connected across'the rails of section AB. 45 The resistor R is adjusted to substantially the same value as it would have for an ordinary track relay of the same resistance and working current as relay P with its full windings 3 and 4 effective. Then, when a train enters this sec- 50 tion, the shunt across the rails which is formed by the wheels and axles causes relay P to release very rapidly becauseonly a portion of the winding of this relay is connected across the rails, and also because of the presence of resistor R As soon as relay P releases, relay S will also release, thereby closing the pickupcircuitforrelayP across the track rails, but as long as any portion of the train occupies section AB, the voltage across windings 3 and 4 will be less than the pickup voltage of relay P. When the entire train leaves section AB, the voltage across windings 3 and. 4 will rise above the pickup value of relay P, so that this relay will close. Relay S will then also close, thereby opening the pickup circuit for relay P and rendering the holding circuit for the latter relay effective. If the train is of light weight and conditions'are such that it provides a high shunting resistance (within limits, of course), it will-still cause relay P to release, Whereas an ordinary track relay might remain in the picked up position. If the resistance of the train shunt varies intermittently, the primary relay P may pick up and release, following the variations in train shunt resistance, without allowing relay S to pick up, due to the slow pickup feature of relay S.

Referring for the moment to Fig. 15 which :shows some construction details of relay S, it will be obvious that relay S is inherently a slow pickup relay for the reason that at the same moment when contact [2 of relay P closes to apply energy to coil 1 of relay S, contact l4 also closes the circuit for retaining coil 9. Conse quently, the building up of flux incore l5, which :tends to attract armature I6, causes a flux to be set up in the retaining core I! whereby armature l9 will be held in contact with the lower portion l8- of pole piece 18, thus retarding the pickup of armature l6 until such time as the .flux in core l reaches .a steady state. On the other hand, when relay P releases, the circuit of the retaining winding 9 is immediately opened andarmature l-6 will release quickly.

Referring again to Fig. 1, it will be apparent in view of the foregoing description that relay S provides'immediate warning when the track circuit is shunted, and at the same time prevents the setting up of a favorable .traffic indication .during a momentary .Iloss of shunt because the .shunt :must be removed from the "track circuit fora'substanti'a'l period oftime before a favorable indication can be :given. To accomplish a similar result with relays .of the ordinary type would require, in place of the single relay S, three relays as follows: One slow pick up secondary relay, one polarized relay, and one slow release repeater of the polarized relay. The parts of Fig. 1 may be so proportioned that the release currentas well as the release voltage 'of the relay combination both approach the pickup current and the pickup voltage, respectively,.so that the combination can be made to produce the maximum shunting sensitivity.

Referring now to Fig. 2, the .apparatusshown in this view is the same as thatshown in 1, except that instead of cutting out a portion-ofthe track relay turns upon pick-up of the secondary relay, the increased shunting sensitivity .is obtainedby connecting one resistor in series with the track relay winding over a front contact of the track relay itself, and connecting another resistor in parallel with the track relay winding as :soon as the secondary relay picks up. The

pickupcircuit for'relayP includes .rail 1, wire 20, winding of relay P, wires 2| and 22, back point vof contact 23 of relay S, and wires and 25 to 31 to rail I 2|, resistor R and wire 31 to rail I noted that whereas in Fig. 2, resistor R is connected across relay P, in Fig. 3, resistor R is conwire 25, to rail I. Across the winding of relay P is connected a. second resistor R over the front point of contact 23 of relay S.

It will be obvious from the foregoing that when the two relays P and S are released, the winding of the primary relay P is connected directly across the track rails, whereas when both of these relays are picked up, the resistor R is included in series with the winding of relay P. This increases the shunting sensitivity but also increases the resistanceof the relay circuit. To compensate for this increase in resistance, the second resistor R is connected in parallel with the Winding of relay P so that the resistance of the relay combination when relay P is picked up remains substantially the same as the resistance of relay P alone.

The apparatus shown in Fig. 2 does not depend upon the adjustment of the track battery limiting resistor, at the minimum ballast resistance, for the amount of flux reduction obtained in relay P when a train enters the section. The battery limiting resistor should be so adjusted as to just obtain working current in relay P under minimum ballast conditions. The values of resistors R and B should be so chosen that the resistance of the combination as viewed from the track circuit will be the same whether relay S is up or down. In this manner, the values .of R and R will depend only on the spread between the pickup and release values of relay P. Consequently, the relay combination can be applied to a track circuit of any suitable length, without readjustment. The parts can be so adjusted that both the release current and. the release voltage of relay P approach the pickup current and pickup voltage of this relay, so that the relay combination can be made to provide the maximum shunting sensitivity on a trackcircuit of any length.

in this figure is the same as that of Fig. 2 with the exception that the front contact 25 of relay P is eliminated. The pickupcircuit for relay P includes rail l, wire 20, winding of relay P, wire 2|, back point of contact 23 of relay S, and wire The holding circuit for relay P includes rail I, wire 2!], winding of relay P, wire It will be nected across the track. Either arrangement can be used, as desired, the results obtained being substantially the same in either case. Contact finger 23 of relay S performs the double function of short-circuiting the series resistor R and opening the circuit of the multiple resistor R Referring to Fig. 4, this figure is the same as Fig. 2 with the exception that resistor R is connected across the track as in Fig. 3 instead of being connected across relay P as in Fig. 2. The pickup and holding circuits for relay P will be obvious from the drawings.

In Fig. 5, I have shown a modification of Fig. 4, in which contact 26 of relay P is eliminated (in the manner of Fig. 3), and resistor R is connected across relay P, over the front point of contact 23 of relay S. The operation of the circuit of Fig. 5 will be clear without further detailed description.

Referring now to Fig. 6, there is shown in this figure a single resistor R having two sections 28 and 29, which resistor replaces the separate re sistors R and R of the foregoing figures. The pickup circuit for relay P includes rail I, wire 23,

winding of relay P, wires 2| and 22, back point of the make-before-break or continuity transfer contact 27 of relay S, and wire 24 to rail I. The holding circuit for relay P includes rail wire 20, winding of relay P, wire 2|, wire 30, front contact 26 of relay P, section 28 of resistor R wire 3|, front point of contact 2! of relay S, and Wire 24 to rail l Section 29 of resistor R is connected across the track over a circuit which includes wire 29, resistor section 28, wire 3|, front point of contact 27 of relay S, and wire 24.

Referring now to Fig. '7, the circuit of this figure is substantially the same as that of Fig. 1 except that the turns of relay P are not decreased when the holding circuit is effective, so that resistor R is connected in series with the full relay winding. It will be understood that the value of resistor R in Fig. '7 must be greater than in Fig. lin order to obtain an equivalent decrease in track relay energization upon pick up.

Referring to Fig. 8, the circuit arrangement of this figure is similar to Fig. 1 except that at pick up, although the full winding of relay P is in the circuit, a portion 32 of this winding is shunted by resistor R The holding circuit for relay P is identical with the corresponding circuit of Fig. 1, in that series resistor R is included, and a portion 32 of the relay winding is excluded, from the circuit.

Referring to Fig. 9, this circuit arrangement is the same as in Fig. 8, except that by using the make-before-break contact 21 of relay S, it becomes possible to open the shunt from around portion 32 of the winding of relay P at pick up, thus permitting the relay to receive its full ampere tum energization under this condition.

In Fig. 10, the circuit arrangement is the same as in Fig. 9, with the exception that the holding circuit for relay P includes the front contact 26 of this relay. The advantage in using front contact 26 is that a stick circuit is provided which insures that once relay P releases, relay S must also release before relay P can receive any current. This avoids the remote possibility of picking up relay P over its holding circuit, should relay S be slow to release and the track energization be high.

Fig. 11 is similar to Fig. except that in Fig. 11 the make-before-break contact 2'! is eliminated by making a minor change in the circuit connections.

Fig. 12 is identical with Fig. 11 except that front contact 26 of relay P is inserted at a different point in the holding circuit.

Referring now to Fig. 13, I have shown in this figure a combination which includes a main primary relay P, an auxiliary relay AP, and the retained neutral armature polarized relay S which has been previously described. The pickup value of relay P is such that under wet ballast conditions, with no train in the section, relay P will pick up but relay AP will remain deenergized. When the ballast dries out relay AP will pick up over the front contact 32 of relay P. The pickup circuit for relay P includes rail wire 2!], Winding of relay P, wires 2| and 22, back contact 5 of relay S, wire 33, back contact 34 of relay AP, and wires 24 and 25, to rail l As soon as relay P picks up, the circuit for resistor R is closed at front contact 35 so that as soon as relay S picks up in turn, resistor R will become effective for decreasing the current supplied to relay P. Prior to the pick up of relay S, if the track voltage is suf ficiently high, relay AP will pick up, causing resistor R to be inserted in series with relay P.

The holding circuitfor relay P will, therefore, extend from rail wire 20, winding of relay P, wires 2| and 35, front contact 35 of relay P, resistors R and R and wires 24 and 25, to rail E Under wet ballast conditions the resistor R will be short circuited by contact 34 of relay AP. When a train enters the section, relay P will be the first to release, followed by relays S and AP, whereupon the pickup circuit just tracedwill become available for picking up relay P as soon as the train clears the section.

Referring to Fig. 14, the circuit of this figure represents a modification of the circuit of Fig. 13. In Fig. 14, relay AP is not permitted to pick up until after relay S has picked up, thus providing a longer time delay before the second resistor R is cut into the circuit and insuring that energy conditions in relay P have become relatively steady before the holding circuit for relay P which includes resistor R is rendered fully effective.

Although the track circuits and track relays are shown in the drawings as being of the direct current type for simplicity, it will be obvious that the invention is not limited to direct current track circuits but may be applied as well to track circuits of the alternating current type, for example. In the latter case, the holding resistor R (as well as other resistors such as R etc.) for the track relay P may be replaced by some other suitabale impedance such as an. in.- ductance or a capacity.

The invention claimed in the present application is an improvement on the apparatus disclosed and claimed in my copending application for Letters Patent of the United States filed on May 31, 1933, Serial No. 673,595, for Railway track circuit apparatus, and on the apparatus disclosed and claimed in an application for Letters Patent of the United States filed by Paul N. Martin on May 31, 1933, Serial No. 673,605, for Railway track circuit apparatus.

Although I have herein described only a few forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, a retaining magnet for'preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across the rails of said section and including a back contact of said secondary relay, a holding circuit for said primary relay connected across said rails and including a resistor, an operating circuit for said secondary relay including a first front contact of said primary relay, and an energizing circuit for said retaining magnet coupled inductively with the operating winding of said secondary relay and including a second front contact of said primary relay.

2. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, a retaining magnet for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit, for said primary relay connected across the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay connected across said rails and including a portion only of the winding of the primary relay, an operating circuit for said secondary relay controlled by said primary relay, and an energizing circuit for said retaining magnet coupled inductively with the operating winding of said secondary relay and also controlled by said primary relay.

3. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, a retaining magnet for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit .for said primary relay connected across the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay connected across said rails and including a portion only of the winding of the primary relay and an impedance, an operating circuit for said secondary relay controlled by said primary relay, and an energizing circuit for said retaining magnet coupled inductively with the operating winding of said secondary relay and also controlled by said primary rela In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across the rails of said section and controlled by said secondary relay, a holding circuit for said primary relay connected across said rails and including a portion only of the winding of the primary relay, and an operating circuit for said secondary relay controlled by said primary relay.

5. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay connected across the rails of said section, a polarized secondary relay having both neutral and polar contacts, an energizing circuit for reversing said secondary relay controlled by said primary relay, means effective when said secondary relay is energized for decreasing the energization of said primary relay to increase the shunting sensitivity thereof, and means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts.

6. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay connected across the rails of said section, a polarized secondary relay having both neutral and polar contacts, an energizing circuit for reversing said secondary relay including a front contact of said primary relay, a pickup circuit for said primary relay including a back contact of said secondary relay, means effective when said secondary relay is energized for decreasing the energization of said'primary relay to increase the shunting sensitivity thereof, and means including a second front :contactof ,said primary relay for prev ting the opening of said neutral contacts during a reversal of said polar contacts.

'7. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a. reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a resistor, and a path around the winding of said primary relay including a front contact of said secondary relay and a second resistor.

8. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a resistor as well as a second front contact of said primary relay, and a path around the Winding of said primary relay including a front contact of said secondary relay and a second resistor.

9. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts. a pickup circuit for said primary relay connected across said rails and efiective when said secondary relay is deenergized, an energizing circuit for said secondary relay controlled by said primary relay, a holding circuit for said primary relay connected across said rails and including an impedance, and means effective when said secondary relay is energized for closing a path including a second impedance around the wind- .ing of said primary relay.

10. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and efiective when said secondary relay is deenergized, an energizing circuit for said secondary relay controlled by said primary relay, and means effective when said secondary relay is energized for by-passing a portion of the current from the winding of said primary relay to increase the shunting sensitivity thereof.

11. In combination with a section of railway contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and effective when said secondary relay is deenergized, an energizing circuit for said secondary relay controlled by said primary relay, and means effective when said secondary relay is energized for connecting an impedance across said rails thereby decreasing the energization of said primary relay to increase the shunting sensitivity thereof.

12. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, .a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a resistor, and means including a front contact of said secondary relay for connecting a second resistor across said rails.

13. In combination with a section of railway track and a. source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected said secondary relay including a front contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a second front contact of said primary relay and a resistor, and means including a front contact of said secondary relay for connecting a second resistor across said rails.

14. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, and a holding circuit for said primary relay connected across said rails and including a resistor as well as a second front contact of said primary relay.

15. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a, polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including the full winding of said primary relay as well as a back contact of said secondary relay, a resistor connected across a portion of said winding through said back contact, an energizing circuit for said secondary relay including a front contact of said primary relay, and a holding circuit for said primary relay connected across said rails and including the remaining portion of the winding of the primary relay and said resistor.

16. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including the full winding of said primary relay as well as a back contact of said secondary relay, a resistor connected across a portion of said winding through said back contact, an energizing circuit for said secondary relay including a front contact of said primary relay, and a holding circuit for said primary relay connected across said rails and including the remaining portion of the winding of the primary relay as well as a second front contact of said primary relay and said resistor.

17. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including the full winding of said primary relay as well as a back contact of said secondary relay, a resistor connected across a portion of said winding through said back contact as well as through a front contact of said primary relay during the pickup interval of said secondary relay, an energizing circuit for said secondary relay including a second front contact of said primary relay, and a holding circuit for said primary relay connected across said rails and including the remaining portion of the winding of said primary relay.

18. In combination with a 'section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a first and a second resistor as well as a second front contact of said primary relay, an auxiliary relay, means effective when said primary relay is energized for energizing said auxiliary relay, and a shunt path around said second resistor including a back contact of said auxiliary relay.

19. In combination with a section of railway track and a source of current connected across the rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a resistor, an auxiliary relay,

meansefiective when said secondary relay is energized for energizing said' auxiliary relay, and means effective when said auxiliary relay is deenergized for short-circuiting said resistor. V

20. In combination with a section of railway track and a source of current connected across the: rails of said section, a primary relay, a polarized secondary relay having both neutral and polar contacts, means controlled by said primary relay for preventing the opening of said neutral contacts during a reversal of said polar contacts, a pickup circuit for said primary relay connected across said rails and including a back contact of said secondary relay, an energizing circuit for said secondary relay including a front contact of said primary relay, a holding circuit for said primary relay connected across said rails and including a resistor as well as a second front contact of said primary relay, an auxiliary relay, means efiective when said secondary relay is energized for energizing said auxiliary relay, and means efiective when said auxiliary relay circuit for said secondary relay including a front contact of said primary relay, aholding circuit for said primary relay connected across said rails and including a first and second resistor as well as a second front contact of said primary relay, an auxiliary relay, means effective when said secondary relay is energized for energizing said auxiliary relay, and a shunt path around said second resistor including a back contact of said auxiliary relay.

E. DODD.

CERTIFICATE OF CORRECTION.

Patent No. 2,065,300. December 8, 1936.

ARTHUR E. DODD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 35, claim 13, strike out the words "said secondary relay including a front and insert instead across said rails and including a back; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of February, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

